1. Field of the Present Disclosure
The present disclosure relates to an image correction data generating apparatus and an image correction data generating program.
2. Description of the Related Art
An image forming apparatus such as a printer or a multi function peripheral performs gamma correction for gradation of image data on the basis of image correction data corresponding to gradation characteristics of an internal printing device. Such gradation characteristics of the printing device change over years, and therefore, this image correction data is updated with performing calibration at a predetermined timing.
In a method (a first method) of the calibration, a test chart which includes plural test patches of different densities is formed on an image carrier on which a toner image is formed; densities of the patches are detected using a sensor; and image correction data is generated from the measurement values of the sensor.
In another method (a second method) of the calibration, test patches are printed on a recording medium; color values of the test patches in a test chart are measured using a reading device such as a scanner; and image correction data is generated from the measurement values.
Since image correction data is generated from colors printed on a recording medium in the second method, in general, the second method performs more precise calibration than the first method.
Since a printer does not include a built-in scanner, in general, the printer performs the calibration in the first method. However, a technique is proposed in which calibration is performed on the basis of image data obtained by an external imaging device such as a digital camera.
In an apparatus (a first apparatus), an RGB value of each patch in a test chart and a reference chart (a chart including patches of known densities) is determined from image data obtained by photographing the test chart and the reference chart using an external imaging device such as a digital camera; and image correction data (a correction formula) is generated from the RGB values of the patches.
Further, in another apparatus (a second apparatus), a test chart and a reference chart are separately photographed using an external imaging device such as a digital camera; and a difference between image data of the test chart and image data of the reference chart is set as a first correction value, and a difference between a measurement density value and a reference density value of each patch in the reference chart is set as second correction values, and the calibration is performed on the basis of these correction values.
However, in the aforementioned first and second apparatuses, due to the image data obtained by photographing the charts using an external imaging device such as a digital camera, RGB values of the image data obtained by photographing change due to changing photography conditions such as a light source and an ambient light. Consequently, it is difficult to precisely perform the calibration.